A mixture containing 3a,6,6,9a-tetramethylperhydronaphto[2,1-b]furan of formula ##STR2## together with minor amounts of its diastereoisomer of formula ##STR3## has been commercialized under the form of a perfume speciality base for over twenty years (FIXATEUR 404.RTM., origin: Firmenich SA, Geneva, Switzerland). The former of the above compounds is better known by its tradename AMBROX (registered trademark of Firmenich SA) whereas the latter is defined by analogy as "iso-AMBROX".
Owing to its typical ambergris character of special radiance, AMBROX has become a perfume ingredient of great usefulness.
Since its discovery [see Helv. Chim. Acta 33, 1251 (1950)], numerous syntheses have been proposed by different research teams. These are generally based on oxidative degradation of diterpenes such as (-)-sclareol or (+)-manool, or employ ambreine as starting material [G. Ohloff in Fragrance Chemistry, ed. Ernst T. Theimer, p. 545, Academic Press (1982)]. These products are all of natural origin and consequently their availability and their quality depend on weather conditions as well as on variable socio-political situations. Yields for their extraction from the natural sources are low and their market price renders their utilization uneconomical. Such a synthetic approach can be illustrated by means of the following simplified reaction pathway: ##STR4## Thus, AMBROX, in spite of its exceptional fragrance properties, has remained so far a product of relatively limited use. The present invention brings a novel and original solution to the challenging problem set by its preparation. By using synthetic raw materials, the process of the invention overcomes the drawbacks of the known methods and constitutes therefore a useful economical alternative from the industrial viewpoint.